Laser Beam Scanning Technique For Optical Phased Arrays

Fiber laser array technology,as an optical phased array technology,can achieve high brightness and high-quality laser output through multi-beam coherent synthesis,which is one of the current research hotspots for high-energy laser systems.At the same time,fiber laser array technology can suppress the turbulence aberration in the atmospheric transmission process,therefore it has a wide application prospect in the fields of longrange space optical communication,directed energy and LIDAR.In order to apply fiber laser array technology to these fields,the fiber laser array needs to have an agile beam pointing capability.At present,the fiber laser array mainly relies on the turntable for beam deflection,which faces the problems of high rotational inertia,inflexibility and high-power consumption,and cannot meet the needs such as modern optical technology for dexterous beam pointing.In this dissertation,the optical phased array scanning technology is taken as the main research content,and a systematic study is carried out for the dexterous beam scanning technology that can be used for fiber laser arrays.The main work and content are as follows.(1)The phase modulation principle of optical phased array scanning technology is analyzed.The mathematical models of the binary grating wavefront phase modulation method and the blazed grating wavefront phase modulation method are established.The mechanism of the two phase control methods for beam scanning is demonstrated by simulation,and the two phase modulation methods are discussed and compared.(2)The optical phased array scanning technology of microlens array has been studied.Through Fourier optics,the mathematical models of microlens array optical phased array with Galileo structure,Kepler structure and the optimized Kepler structure are established respectively.The simulation results show that under the same parameters,the Kepler structure has the simplest structure and the largest scanning FOV(field of view),the Galileo structure has the most compact structure and no internal focus,and the optimized Kepler structure has the highest energy utilization.(3)The Kepler structure microlens array optical phased array scanning technology is experimentally studied.The relationship between the relative displacement between the microlens array and the scanning angle,the discrete angular width,the scanning point angular spacing,the spot morphology,the discrete addressing scanning and other key parameters and phenomena are experimentally verified,and the experimental results are consistent with the theoretical analysis.(4)The cascaded continuous addressing scanning technology using an adaptive fiber collimator as a pre-scanning device is proposed to address the problem that the microlens array optical phased array can only achieve discrete addressing scanning due to the phase modulation of the blazed grating.The mathematical model of continuous addressing scanning realized by the cooperative work of adaptive fiber collimator and microlens array optical phased array is established.Formulas are derived for the conditions to be met for the two devices to work together.An experimental platform based on adaptive fiber collimator and Kepler microlens array optical phased array is built,and the experimental research is carried out.The continuous addressing scanning of diffraction limit level is realized,which is consistent with the theoretical and simulation results.(5)A method to realize continuous addressing scanning by using the piston and tilt phase modulation capability of fiber laser array is proposed.A mathematical model for beam scanning using piston phase modulation and tilt phase modulation is established and theoretically analyzed.In view of the hysteresis and non-linearity of the piezoelectric actuators used in the fibre laser array,a continuous tracking and targeting method is proposed using the target-in-the-loop technique to control the piston and tilt phase of the fibre laser array by feed-back.The experimental system of seven fiber laser arrays is built and the target-in-the-loop technology based on stochastic parallel gradient descent algorithm is used to achieve continuous tracking and targeting of moving targets.